Monosilane is useful as a volatile silicone material having high purity, and has been widely used for producing solar cells, semiconductors, amorphous photosensitive silicone materials and various ceramic materials.
Various methods for producing monosilane have been known to date. A method using reaction between magnesium silicide and acid or ammonium bromide, a method by reducing silicon chloride using LiAlH4, a method by reducing silicon tetrafluoride using CaH2 and a method by disproportionation reaction of alkoxysilane have been known.
Trialkoxysilane is generally used as a starting material in the disproportionation reaction of alkoxysilane, and monosilane and tetraalkoxysilane are produced according to the formula as follows:4HSi(OR)3→SiH4+3Si(OR)4   [Chem. 1]
Like monosilane, tetraalkoxysilane is a useful chemical substance as a pure silicon precursor material for producing various silicon compounds for optical fibers, photomasks and IC sealing materials.
Triethoxysilane and trimethoxysilane are used as a starting material in the above-mentioned disproportionation reaction and tetraethoxysilane and tetramethoxysilane are produced at the same time as monosilane, respectively, as shown in the following formulae.4HSi(OMe)3→SiH4+3Si(OMe)4 4HSi(OEt)3→SiH4+3Si(OEt)4 [Chem. 2]
When the above reaction is conducted, metal sodium can be used as a catalyst of the disproportionation reaction. However, the yield is low in the reaction and therefore the method was not practically useful.
Patent Document 1 (U.S. Pat. No. 4,016,188) discloses a method using alkali metal alkoxide or alkali metal silicate as a catalyst. However, the reaction in a liquid phase is too slow such that the reaction time exceeds ten hours, and therefore the method is not suitable for industrial production.
Patent Document 2 (JP-A-2001-19418) discloses a method for producing monosilane and tetraalkoxysilane by disproportionation of alkoxysilane represented by formula HnSi(OR)4−n wherein n is 1, 2 or 3 and R represents alkyl group or cycloalkyl group, comprising (i) a reaction step of obtaining monosilane and tetraalkoxysilane by disproportionation of alkoxysilane in a solvent in the presence of a catalyst, (ii) a step of extracting part of the solvent containing a catalyst and tetraalkoxysilane from the reaction step, and (iii) a step of separating part or all of the tetraalkoxysilane by distilling the extracted solvent containing a catalyst and tetraalkoxysilane.
However, the method also employs disproportionation reaction in a solution and has a problem of difficulties in separation from the solvent and a problem of insufficient reaction rate.
Patent document 3 (WO 2008/042445 pamphlet) discloses a method for producing monosilane and tetramethoxysilane by disproportionation of trimethoxysilane on a potassium fluoride (KF) loaded alumina catalyst. Although this method has no problem with a separation of the catalyst and the like from the reaction products, conversion of trimethoxysilane is not sufficiently high.